1. Field of the Invention
The present invention relates to a drive for a refill for a ballpoint pen having a driving axial tube and driving casing tube with a continuous groove and a projection engaged therein so that the cap of the pen can continuously rotate by 360.degree. in both the positive or negative direction in order to achieve the function of freely extending or retracting a ballpoint refill.
2. Description of the Prior Art
For a conventional writing tool of the telescopic ballpoint pen type, there are two types of telescopic control of the ballpoint refill, namely, the contact compression type and the rotation driving type. Although there are many types of rotation driving structures for the ballpoint refills, the general defects are that they have too many elements and too complicated a structure, thus causing a combination of inconvenience and too high cost. Moreover, in operation and use, the conventional rotation driving structures for the ballpoint refill are mostly of the type for single direction rotation driving for extension of the ballpoint refill and reverse direction rotation to retract the ballpoint refill if desired, i.e. the extension or retraction of the ballpoint refill cannot be achieved by continuously rotating the cap of the pen through 360.degree. but must be achieved by reciprocal rotating operations, thus causing much inconvenience in use. In addition, improper attempts to rotate the structure in the wrong operational direction may cause damage to the driving system. Further, at the present time, the specification of the ballpoint refills for a higher grade of pens can be classified in two major systems, namely the systems respectively used in pens sold under the trademarks PARKER and CROSS. As the conventional ballpoint pens are restricted to their inherent structures, they can only use refills of given specifications, and refills other than those meeting the originally used specifications cannot be used, thus causing the burden and annoyance to users of purchasing only limited types of refills.